U.S. patent application number 10/727620 was filed with the patent office on 2004-07-15 for developing apparatus.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Kakimoto, Hiroaki.
Application Number | 20040136755 10/727620 |
Document ID | / |
Family ID | 32708078 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040136755 |
Kind Code |
A1 |
Kakimoto, Hiroaki |
July 15, 2004 |
Developing apparatus
Abstract
The present invention relates to a developing apparatus for
developing an electrostatic image formed on an image carrier,
comprising a developing container, a first developing member formed
at the first chamber for conveying developer to a first developing
portion, a second developing member provided with the second
chamber for conveying the developer to a second developing portion
and a magnetic field generating means for generating magnetic field
for transferring the developer between the first developing member
and the second developing member. The diaphragm is disposed in a
non-contacting manner to the first developing member and the second
developing member and has a restricting member for restricting
entry of the developer out of an interior of the developing
container to a space between the first developing member and the
second developing member.
Inventors: |
Kakimoto, Hiroaki;
(Kanagawa-ken, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
32708078 |
Appl. No.: |
10/727620 |
Filed: |
December 5, 2003 |
Current U.S.
Class: |
399/269 |
Current CPC
Class: |
G03G 2215/0177 20130101;
G03G 15/0898 20130101 |
Class at
Publication: |
399/269 |
International
Class: |
G03G 015/09 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2002 |
JP |
356575/2002 (PAT |
Claims
What is claimed is:
1. A developing apparatus for developing an electrostatic image
formed on an image carrier, comprising: a developing container for
containing a magnetic developer, the developing container being
portioning into a first chamber and a second chamber constituting a
circulation path of the developer, the first chamber being disposed
on an upper side of the second chamber; a first developing member,
provided with the first chamber, for supplying the developer to the
electrostatic image on the image carrier; a second developing
member, provided with the second chamber, for supplying the
developer to the electrostatic image on the image carrier; and a
magnetic field generating means for generating magnetic field for
transferring the developer between the first developing member and
the second developing member on the image carrier side, a
restricting member for restricting entry of the developer in the
developing container to a space between the first developing member
and the second developing member, the restricting member is
disposed in a non-contacting manner to the first developing member
and the second developing member.
2. The developing apparatus according to claim 1, wherein the
restricting member is provided extending substantially along a
circumferential surface of the second developing member.
3. The developing apparatus according to claim 1 or claim 2,
wherein the magnetic field generating means has a pair of magnetic
polarities disposed stationarily in the second developing member
for forming a resilient magnetic field, and the restricting member
is arranged to protrude in a manner non-contacting but adjacent to
the magnetic polarity pair.
4. The developing apparatus according to claim 3, wherein the first
developing member carries the developer in the first chamber and
conveys the developer to the image carrier, and wherein the second
developing member carries the developer received from the first
developing member and conveys the developer to the image
carrier.
5. The developing apparatus according to claim 1, wherein the
restricting member is provided extending substantially along
circumferential surfaces of the first developing member and the
second developing member.
6. The developing apparatus according to claim 1 or claim 5,
wherein the magnetic field generating means has a pair of magnetic
polarities disposed stationarily in the first developing member for
forming a resilient magnetic field and a pair of magnetic
polarities disposed stationarily in the second developing member
for forming a resilient magnetic field, and the restricting member
is arranged to protrude in a manner non-contacting but adjacent to
the magnetic polarity pairs.
7. The developing apparatus according to claim 6, wherein the first
developing member carries the developer in the first chamber and
conveys the developer to the image carrier, and wherein the second
developing member carries the developer received from the first
developing member and conveys the developer to the image
carrier.
8. The developing apparatus according to claim 1, wherein the
restricting member has a portioning portion for portioning the
developing container into the first chamber and the second
chamber.
9. The developing apparatus according to claim 1, wherein the
magnetic developer includes a non-magnetic toner and a magnetic
carrier.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a developing apparatus for
developing electrostatic images formed on an image carrier using,
e.g., an electrophotographic method, an electrostatic recording
method and, more particularly, to an apparatus used for
photocopiers, printers, and facsimile machines.
[0003] 2. Description of Related Art
[0004] Conventionally, color image forming apparatuses have been
well known in which having plural developing apparatuses containing
respectively developers of different colors and obtaining
multicolor images using electrophotographic methods.
[0005] Referring to FIG. 3, described is a main cross-sectional
structure of a conventional multicolor image forming apparatus.
Exemplified herein as a conventional multicolor image forming
apparatus is that four-color developing apparatuses are contained
in a rotary body, which rotates by a prescribed angle at developing
operation of respective colors to develop properly the images of
respective colors.
[0006] In this prior art, the developing apparatus has a feature
equipped with two developing rollers for respective colors, and the
developer contains a two-component made of a so-called carrier
serving as a magnetic agent and a toner for actually developing the
latent image.
[0007] In this color image forming apparatus, an image processing
means is constituted of a photosensitive drum 1 serving as an image
carrier, a primary charger as a charging means, a laser scanner
providing image information, a rotary type developing apparatus 5
supporting developing devices 4a, 4b, 4c, 4d as four developing
means, an intermediate transfer body 6, and a cleaning apparatus
collecting transfer remaining toner.
[0008] The image processing means ensures a size in the
longitudinal direction corresponding to a prescribed length in the
longitudinal direction of the photosensitive drum 1 required for
image formation of a prescribed width.
[0009] The rotary type developing apparatus is of a type settling
one of four developing devices 4a to 4d to a developing position
according to the rotation of a supporting body 9. The rotary type
developing apparatus 5 has development opening surfaces for the
respective developing devices 4a to 4d on a circumference of a
circle whose center is at a support body rotary shaft 8.
[0010] The developing devices 4a to 4d have first developing
rollers 10a, 10b, 10c, 10d and second developing rollers 11a, 11b,
11c, 11d serving as rotary developer carriers for conveying the
toner to a portion contacting to the photosensitive drum 1.
[0011] The rotary type developing apparatus 5 has a structure that
only during the developing operation the first developing rollers
10a, 10b, 10c, 10d and the second developing rollers 11a, 11b, 11c,
11d in the developing devices 4a to 4d are made closer to the
photosensitive drum 1 within a prescribed amount by moving the
developing devices 4a to 4d with positioning apparatuses 12a, 12b,
12c, 12d and that during the rotation of the rotary type developing
apparatus 5 as well as during non-development operation the first
developing rollers 10a, 10b, 10c, 10d and the second developing
rollers 11a, 11b, 11c, 11d in the developing devices 4a to 4d are
isolated from the photosensitive drum 1 by releasing the contacting
operation of the positioning apparatuses 12a, 12b, 12c, 12d.
[0012] Referring to FIG. 4 and FIG. 5, the developing device
positioning apparatus for the rotary type developing apparatus in
FIG. 3 is described. Numeral 20 denotes a photosensitive drum;
numeral 21 denotes a support body of a rotary type developing
apparatus 22; numeral 23 denotes a developing device. The
developing device 23 is mounting a first developing roller 24 and a
second developing roller 25. The developing device 23 is installed
movably on a developing guide 26. The developing guide 26 is set so
that the first developing roller 24 and the second developing
roller 25 are movable parallel to the surface of the photosensitive
drum 20 up to coming closer in a prescribed amount. Numeral 27 is a
positioning cam and move pivotally around a pivotal shaft 28. A
roller 29 is disposed rotatably at a tip thereof.
[0013] The rotary type developing apparatus 22 rotates the
developing device 23 by a rotary driving means, not shown, to a
prescribed position on the photosensitive drum 20 at which the
electrostatic latent image can be developed. The positioning cam is
rotated in arrow B direction in the drawing with a drive apparatus,
not shown, around the pivotal shaft 28. According to this rotation,
the developing device 23 moves in arrow C direction in the drawing
and reaches the state shown in FIG. 5.
[0014] In FIG. 5, a part of a container 30 hits a hitting member,
not shown, of the supporting body 21 to cease the developing device
23, so that the developing device 23 is held as it is according to
holding force of the positioning cam 27. With this state, the first
developing roller 24 and the second developing roller 25 of the
developing device 23 can come closer to the prescribed amount such
that the electrostatic latent images on the photosensitive drum 20
can be properly developed. The prior art has a structure that this
prescribed amount is in a range from 200 microns to 400
microns.
[0015] Next, a process for forming color images on a transfer
material using this color image forming apparatus is described.
[0016] The photosensitive drum 1 is rotated in arrow A direction,
and the primary charger charges the drum uniformly. Exposure 13 by
the laser scanner 3 then forms electrostatic latent images on the
photosensitive drum 1. These latent images are corresponding to
color developers in the developing devices 4a to 4d, or namely
respective colors such as yellow (Y), magenta (M), cyan (Y), and
black (Bk).
[0017] Regarding to the first color, the electrostatic latent image
corresponding to, e.g., the yellow developer is formed on the
photosensitive drum 1, and the image, after visualized with the
known process among the developer carriers 10a, 11a of the
developing device 4a in which the yellow developer is contained,
and the photosensitive drum 1, is transferred with a first transfer
roller 14 to the intermediate transfer body 6.
[0018] Subsequently, after the remaining toner on the
photosensitive drum 1 is cleaned up with the cleaning apparatus 7
such as a blade or the like, the electrostatic latent image
corresponding to, e.g., the developer, as the second color, is
formed on the photosensitive drum 1, and the image, after
visualized with the known process among the developer carriers 10a,
11a of the developing device 4a in which the magenta developer is
contained, and the photosensitive drum 1, is transferred in an
overlapping manner with the first transfer roller 14 to the
intermediate transfer body 6 to which the yellow visualized image
of the first color is transferred.
[0019] After the above operations are done in a plural number, the
toner overlapped as plural layers on the intermediate transfer body
6 is transferred onto a transfer material P as described below.
[0020] Hereinafter, the step that the toner of the plural layers on
the intermediate transfer body is transferred onto the transfer
material P is described.
[0021] A transfer material 102 stacked on the cassette 101 in FIG.
3 is fed out with a pickup roller 103, and the topmost transfer
material P2 is solely transferred on a downstream side by a feeding
roller 104 and a reverse separation roller 105 rotating in the
reverse direction to the feeding direction. The transfer material
P2 is then conveyed along the conveyance path by plural conveyance
roller pairs 106, and is bent upon front end's engagement with a
nipping portion of a stopped registration roller pair 107, thereby
being corrected from obliquely feeding.
[0022] The registration roller pair 107 begins rotating at a timing
synchronized with a toner image formed on the intermediate transfer
body 6, thereby feeding out the transfer material. The fed transfer
material enters in the nipping portion formed with the intermediate
transfer body 6 and a second transfer roller 108, and the toner
image on the intermediate transfer body is transferred to the
transfer material (P1 in FIG. 3).
[0023] The transfer material P1 is then conveyed with a conveyance
belt 109 to a fixing apparatus 110 made of two rollers, located on
upper and lower sides. The toner image on the transfer material at
the fixing apparatus is fixed to the transfer material, and is
delivered to a delivery tray 112 via a delivery roller 111.
[0024] Such a color image forming apparatus has been proposed as an
example of a color image forming apparatus particularly for higher
image quality than the usual image quality. Such an apparatus has a
feature that each of the four-color developing devices contained in
the rotary body is mounting two developing rollers. Described
herein as an example of such an apparatus feature is that the
four-color developing devices contained in the rotary body have the
same shape and the same mass and are disposed equally with 90
degrees spaced with respect to a rotary center of the rotary
body.
[0025] Next, the developing device in the rotary body is
described.
[0026] FIG. 6 and FIG. 7 show two states taken by the developing
device in the rotary body 40. In FIG. 7, numeral 41 shows a
photosensitive drum, and FIG. 7 shows a situation that the
electrostatic latent image of the photosensitive drum is developed
by an developer of the developing device 42. The rotary body 40 has
a structure to rotate by each of 90 degrees in the counterclockwise
direction (arrow D in the drawing). FIG. 6 shows the state that the
rotary body is located at a position of -90 degrees in the
rotational direction of the rotary body (rotational direction of
the rotary body is defined as "+") with respect to the developing
position shown in FIG. 7.
[0027] In reference to FIG. 6, an internal structure of the
developing device 42 is described. The developing device 42 has a
first developing roller 44 and a second developing roller 45, and
each of the developing rollers has a first developing sleeve and a
second developing sleeve, which are in a rotatable state with a
drive mechanism, not shown, and a first magnet roller 48 and a
second magnet roller 49 stationally formed at respective centers of
the developing rollers.
[0028] As shown in FIG. 6, the magnetic polarity arrangement of the
first magnet roller 48 and the second magnet roller 49 is such that
the north polarity and the south polarity are set entirely reverse
to each other.
[0029] In the developing device 42, the first screw 50 and the
second screw 51 are disposed. A diaphragm 53 structured by a part
of a container 52 is projected between the first screw 50 and the
second screw 51, thereby forming a developing chamber 54 enclosed
with the first developing roller 44 and a stirring chamber 55
enclosed with the second developing roller 45, respectively. The
opposite ends in the longitudinal direction of the first screw 50
and the second screw 51 are supported to bearings, not shown.
[0030] For the purpose of the explanation, the space between the
first developing roller 44 and the second developing roller 45 is
defined as an SS space 56.
[0031] A situation shown in FIG. 6 is described. As described
above, FIG. 6 shows the state of -90 degrees with respect to the
developing position, and in this state, the first developing roller
44 and the second developing roller 45 are positioned on a
substantially lower side, and therefore, a developer 57 existing in
the developing device 42 is deposited as to overlap the first
developing roller 44 and the second developing roller 45 by
operation of the gravity force as shown with "circle patterns" in
FIG. 6. From another viewpoint, the developer is attracted by
magnetic force of the first magnet roller 48 and the second magnet
roller 49 in the first developing roller 44 and the second
developing roller 45, and a space including the SS space 56, other
than an empty space at an upper portion of the developing chamber
54 and the stirring chamber 55, is filled with the developer 57 by
a synergy effect with the above gravity force.
[0032] Next, the state shown in FIG. 7 is described below. As
described above, FIG. 7 shows a state for developing position, and
in this state, the first developing roller 44 and the second
developing roller 45 are in a drive state, while the first
developing sleeve 46 and the second developing sleeve 47 rotate in
directions of arrows E, F.
[0033] Regarding the first screw 50 and the second screw 51, as
shown in the drawing in respect with the developer in the
developing device 42, the lead and rotational direction of the
first screw 50 is set so that the developer is conveyed in a
direction toward the front side of the drawing, and similarly, the
lead and rotational direction of the second screw 51 is set so that
the developer is conveyed in a direction toward the rear side of
the drawing. The developing chamber 54 containing the first screw
50 and the stirring chamber 55 containing the second screw 51 are
structured to communicate with each other at the opposite ends in
the longitudinal direction.
[0034] Referring to FIG. 8, the flow of the developer 57 existing
in the developing device 42 is described. FIG. 8 is a schematic
view showing a cross section along an axial line extending in the
longitudinal direction of the developing device 60. Numeral 61
denotes a first screw described in FIG. 6, 7; numeral 62 denotes a
second screw; numeral 63 denotes a developing chamber containing
the first screw; numeral 64 denotes a stirring chamber containing
the second screw. Numeral 65 denotes a toner hopper for supplying a
toner to the developing device 60.
[0035] One flow is for equalizing the toner density of the
developer in the developing device 60. The toner 66 supplied from
the toner hopper 65 is supplied to the developing device 60 from
extension 641 of the stirring chamber 64 and conveyed in the
stirring chamber 64 in arrow direction of arrows G, H as stirred
with the carrier in the stirring chamber 64 and as maintaining the
state of the developer. The toner at that time receives further
triboelectric charges from adequate stirring with the carrier.
[0036] The developer is overly filled at an end 642 of the stirring
chamber 64 because the developer is sent to the second screw 62.
The end 642 of the stirring chamber is structured with a
communication path 67 in communication with the end 632 of the
developing chamber, so that overly filled developer enters toward a
side of the end 632 of the first developing chamber 63.
[0037] The first screw 61 of the developing chamber 63 conveys the
developer in the first developing chamber in a direction of arrow I
in the drawing. The developer conveyed in the developing chamber 63
reaches the other end 631 of the developing chamber. Another
communication path in communication with the stirring chamber is
formed even at the other end 631 of the developing chamber, so that
the developer is circulated into a merging portion 643 of the
stirring chamber 64 again.
[0038] Other flows of the developer are used for a process
developing the electrostatic latent image on the photosensitive
drum with the developer in the developing device. This flow is
described with reference to FIG. 7.
[0039] As shown in FIG. 7, the developer 571 in the developing
chamber 54 faces to the first developing roller 44, and a part of
the developer 571 conveyed thereto is fed around the surface of the
first developing sleeve 46 by magnetic attracting force of the
first magnet roller 48 of the first developing sleeve 44, and is
carried as a thin layer with a restricting blade 58. The developer
develops the electrostatic latent image on the surface of the
photosensitive drum 41 according to the rotation of the first
developing sleeve 46 and further conveyed to the second developing
roller 45.
[0040] As a feature of the magnetic polarity arrangement of the
first magnet roller 48 and the second magnet roller 49, the
magnetic flux density is made higher at a space between the N1
polarity 481 of the first magnet roller 48 and the S2 polarity 491
of the second magnet roller 49 because the N1 polarity 481 of the
first magnet roller 48 and the S2 polarity 491 of the second magnet
roller 49 are arranged as opposed to each other, so that transfer
of the developer can be done surely from the first developing
sleeve 44 to the second developing sleeve 47, and so that the toner
and the carrier can be prevented from scattered between the
sleeves.
[0041] The second developing roller 45 carries the developer to the
surface of the second developing sleeve 47 in substantially the
same manner by the magnetic attracting force of the second magnet
roller 49. The developer on the surface of the second developing
sleeve 47 performs the second development of the electrostatic
latent image on the photosensitive drum 41. Accordingly, the twice
developments with the first developing roller 44 and the second
developing roller 45 render the developer enter into the stirring
chamber 55 in the developing device 42 again in a state that the
toner density of the developer is lowered. In the second developing
chamber 55, the developer 572 stirred and conveyed by the second
screw 51, exists and merges with the developer.
[0042] In a meantime, as described above, almost all of the space
including the SS space is filled with the developer 57 by the
synergy effect of the gravity force and the magnetic force of the
two magnet rollers.
[0043] If the rotary body is rotated to a developing position shown
in FIG. 7 from this state, the developer 57 in the developing
device 42 is located in a range shown with "circle patterns" and
"dot patterns" in the drawing.
[0044] Regarding to the developer of "circle patterns" in FIG. 7,
as shown as the prior art, while the agent is circulated by the two
developing screws in the developing device 42, a part of the agent
is carried with two developing rollers to contribute the
development of the electrostatic latent image on the photosensitive
drum.
[0045] On the other hand, the portion shown with "dot patterns" in
FIG. 7 is a portion defined as the SS space in FIG. 6 and is a
portion at which the developer 573 is carried by magnetic force of
the two magnet rollers. In this SS space 56, the S2 polarity 482 of
the first magnet roller 48 and the N1 polarity 492 of the second
magnet roller 49 are arranged as to be opposed to each other, so
that the magnetic flux density is made higher between the
polarities, and so that the SS space 56 is subject to higher
constraint force against the developer by the magnetic force.
[0046] The developer 573 is a agent that is circulated into the
stirring chamber after the developing operation of the previous
time and that is contained in the stirring chamber. That is, the
developer 573 is a developer with a reduced toner density, which is
entirely different from the developer passing through the
restricting blade 58 under the regular process. In the state shown
in FIG. 6, the developer enters into the SS space.
[0047] The developer 573 carried in the SS space 56 is conveyed to
the second developing sleeve 46 again as shown in arrow K in FIG.
7, and the coating amount of the developer of the second developing
sleeve 46 greatly excesses the coating amount of the first
developing sleeve 46 normalized with the restricting blade 58.
[0048] With such a state that the developer is mixed, not only
defective image such as reduced density after duration may be
formed, but also the coating amount of the second developing sleeve
46 itself becomes greatly larger than the proper amount, in the
developing process of the electrostatic latent image on the
photosensitive drum 41, thereby raising various problems such that
blurs and overflows from the developing container 52 simply occur
to scatter the toner in the device.
[0049] This invention is made in consideration with the above
problems. It is an object to provide a developing apparatus
avoiding a developer to be coated more than the necessary amount on
a developing roller to prevent blurs and overflows out of a
container from occurring and to obtain developed images with high
quality.
SUMMARY OF THE INVENTION
[0050] It is an object of the invention to provide a developing
apparatus capable of restricting entry of a developer into a space
between a first developer carrier and a second developer
carrier.
[0051] It is another object of the invention to provide a
developing apparatus, without reducing the duration of the first
developer carrier and the second developer carrier, capable of
restricting entry of a developer into a space between a first
developer carrier and a second developer carrier.
[0052] It is yet another object of the invention to provide a
developing apparatus for developing an electrostatic image formed
on an image carrier, comprising: a developing container containing
a magnetic developer; a diaphragm substantially portioning the
developing container into a first chamber and a second chamber
constituting a circulation path of the developer, the first chamber
being disposed on an upper side of the second chamber; a developing
container for containing a magnetic developer, the developing
container being portioning into a first chamber and a second
chamber constituting a circulation path of the developer, the first
chamber being disposed on an upper side of the second chamber;
[0053] a first developing member, provided with the first chamber,
for supplying the developer to the electrostatic image on the image
carrier;
[0054] a second developing member, provided with the second
chamber, for supplying the developer to the electrostatic image on
the image carrier; and
[0055] a magnetic field generating means for generating magnetic
field for transferring the developer between the first developing
member and the second developing member on the image carrier
side,
[0056] a restricting member for restricting entry of the developer
in the developing container to a space between the first developing
member and the second developing member, the restricting member is
disposed in a non-contacting manner to the first developing member
and the second developing member .right brkt-bot.. restricting
member Further objects of the invention will be apparent from
reading the following detailed description in reference to the
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] FIG. 1 is a diagram showing a state that a developing device
is isolated from a photosensitive drum according to the
invention;
[0058] FIG. 2 is a diagram illustrating a flow of a developer in
the developing device according to the invention;
[0059] FIG. 3 is an illustration showing a color image forming
apparatus mounting a rotary type developing apparatus;
[0060] FIG. 4 is a diagram showing a pre-operation state of a
development positioning apparatus at a developing position;
[0061] FIG. 5 is a diagram showing a post-operation state of the
development positioning apparatus at the developing position;
[0062] FIG. 6 is a diagram showing a state in which a conventional
developing device is isolated from a photosensitive drum;
[0063] FIG. 7 is a diagram showing a flow of a developer in the
conventional developing device;
[0064] FIG. 8 is a diagram showing a flow of a developer in a cross
section along a longitudinal direction of the conventional
developing device;
[0065] FIG. 9 is an illustration showing another embodiment of the
color image forming apparatus mounting a developing apparatus
according to the invention; and
[0066] FIG. 10 is a detailed diagram showing the interior of the
developing device in FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] Hereinafter, referring to the drawings, the preferred
embodiments of the invention are described in detail in an
exemplifying manner. Size, material, and shape of structural parts
as set forth in the embodiments below, and correlated arrangement
of those parts can be modified properly according to the
constitution of the apparatus to which this invention applies and
various conditions, and as far as no special description is made,
it is not intended that the scope of the invention is limited to
those embodiments only.
FIRST EMBODIMENT
[0068] An embodiment of the invention is described in FIG. 1 and
FIG. 2. It is to be noted that the schematic structure of the image
forming apparatus having the developing apparatus according to this
embodiment is substantially the same as that of the prior art, and
therefore, a detailed description is omitted. With respect to the
members commonly used in the prior art, reference numbers used in
the prior art are used as they are, and a detailed description is
omitted.
[0069] FIG. 1, FIG. 2 are for showing two states taken by a
developing device 42 in a rotary body 40. FIG. 1 is for a state
that the developing device 42 is located at a position of -90
degrees with respect to a rotational direction of the rotary body
40 prior to the developing position; FIG. 2 shows the developing
position.
[0070] The state shown in FIG. 1 is described. With this situation,
a first developing roller 44 serving as a first developer carrier
(first developing member) and a second developing roller 45 serving
as a second developer carrier (second developing member) are
located on a lower side, so that a developer 57 existing in the
developing device 42 is deposited according to operation of gravity
force as to overlap the first developing roller 44 and the second
developing roller 45 as shown with "circle patterns" in FIG. 1.
[0071] In this embodiment, a diaphragm 53 constituted of a part of
the developing container 52 in the developing device 42 is
protruded to form a developing chamber 54 enclosed with the first
developing roller 44 and a stirring chamber 55 enclosed with the
second developing roller 45, respectively.
[0072] A restricting member 70 for restricting entry of the
developing apparatus agent into an SS space as a region between the
first developing roller 44 and the second developing roller 45 is
arranged as to continue to the diaphragm 53 where the front end of
the diaphragm 53 is widened.
[0073] With this structure, in this embodiment, the developer in
the SS space can be avoided from attracted by the magnetic force of
a first magnet roller 48 and a second magnet roller 49 in the first
developing roller 44 and the second developing roller 45 from
operation of the restricting member 70.
[0074] Flow of the developer at the developing position is
described next. In this embodiment, the cross-sectional structure
of the developing device along the longitudinal direction is equal
to what is shown in the prior art (see FIG. 8), duplicated
description is omitted. The flow of the developer is basically the
same as that of the prior art, which is for unifying the toner
density of the developer in the developing device 42 and for used
in a process developing electrostatic latent images on the
photosensitive drum with the developer in the developing device
42.
[0075] Herein, particularly, flow of the developer with respect to
the developing process is described. As shown in FIG. 2, the
developer 571 in the developing chamber 54 reaches the surface of
the first developing sleeve 46 in the same way as in the prior art
and is carried as in a thin layer shape by means of the restricting
blade 58. The developer 571 is then transferred to the second
developing sleeve 47 as developing the electrostatic latent images
on the surface of the photosensitive drum 41.
[0076] The developer carried on the surface of the second
developing sleeve 47 performs the second development on the
electrostatic latent images on the photosensitive drum 41, and
enters in the second developing chamber 55 in the developing device
42 as in a state that the toner density is lowered to merge with
the developer 572, which is stirred and conveyed by the second
screw 51.
[0077] As described with FIG. 1, because the front end of the
diaphragm 53 is widened and because the restricting member 70 for
restricting the entry of the developer into the SS space located
between the first developing roller 44 and the second developing
roller 45 is disposed, the entry of the developer into the SS space
56 is prevented. It is to be noted that the diaphragm is not formed
as to completely partition between the developing chamber and the
stirring chamber, and the developing chamber and the stirring
chamber are formed with a communication path permitting passage of
the developer around the vicinity of the opposite ends in the
longitudinal direction as to constitute a circulation path of the
developer.
[0078] The shape of the restricting member 70 is described in
detail. As other features of the magnetic arrangement of the first
magnet roller 48 and the second magnet roller 49 as described
above, the S2 polarity 482 and S1 polarity 483, which are magnetic
polarities of the same polarity adjacent to each other, are
disposed at the first magnet roller 48. This is a known technology
that the magnet polarities of the same polarity are disposed
parallel so that the developer does not come around from the S2
polarity side on the upstream side in the rotational direction of
the first developing sleeve 46 to the S1 polarity side to separate
the developer from the surface of the first developing sleeve 46 at
a so-called "magnetic flux zero point" 484 (shown with a single
dotted line) at which no magnetic flux exists between both of the
polarities.
[0079] In substantially the same way, the N2 magnetic polarity 493
and the N1 magnetic polarity 492, magnetic polarities adjacent to
each other, are arranged at the second developing magnet roller 49,
thereby rendering the magnetic flux null at the "magnetic flux zero
point" 494 (shown with a single dotted line) located between the
magnetic polarities to separate the developer from the surface of
the second developing sleeve 47.
[0080] The restricting member is desirably positioned most closely
to the first developing sleeve 46 and the second developing sleeve
47 at the "magnetic flux zero point" 484, 494 described above. In
this embodiment, a part of the restricting member 70 is extending
to a position 71 with respect to the "magnetic flux zero point"
484, whereas extending to a position 72 with respect to the
"magnetic flux zero point" 494, thereby realizing the structure
described above.
[0081] This structure can form a structure that the developer
little enters into the space between the restricting member and
sleeve surface at a position of the least magnetic flux amount on
the developing roller, so that with the synergy effect, the
entering amount of the toner can be suppressed to the minimum
amount to the SS space 56.
[0082] The restricting member 70, at least, may be desirably formed
to have the narrowest space to the sleeve around the "magnetic flux
zero point" even where not reaching the positions 71, 72 as in this
embodiment.
[0083] According to an experiment, by setting the space at the
closest position between the restricting member described above and
the sleeve to 2 mm or lower, an advantage was obtained for
prevention of entry of the developer to the SS space 56.
[0084] With the structure described above, even where the
developing device 42 moves to the developing position in FIG. 2,
the developer still does not enter into the SS space 56. That is,
the developer deteriorated may not be re-coated on the second
developing roller 45.
[0085] As described above, according to the embodiment, since the
restricting member 70 is disposed for restricting the entry of the
developer to the region (the SS space 56) sandwiched between the
first developing roller 44 and the second developing roller 45
extending adjacent to each other as well as the region of the
interior of the developing container 52, the developer may not
enter into the SS space 56 serving as the above region, so that the
developer is avoided to be coated more than the necessary amount on
the second developing roller 45, and so that blurs and overflows
from the developing container 52 are prevented to bring developing
images with higher quality.
SECOND EMBODIMENT
[0086] This invention is not limited to the rotary type image
forming apparatus described above, and is applicable to an inline
type image forming apparatus in which four developing devices are
arranged. It is to be noted that because the image forming
apparatus shown in FIG. 9 has substantially the same structure as
that of the first embodiment except the developing devices are
arranged parallel, members and apparatuses having the same
functions are assigned with the same reference numbers, and a
detailed description is omitted.
[0087] FIG. 10 shows a detailed structure of the developing
apparatus shown in FIG. 9. The outline of the developing apparatus
is as follows: the developing container is partitioned to, as upper
and lower, a developing chamber and a stirring chamber with the
diaphragm (the stirring chamber is located on a lower side of the
developing chamber in the gravity force direction), and a magnetic
developer having a non-magnetic toner and a magnetic carrier is
sent to a developing chamber 63 upon pushed up by a second screw 51
at a path 67 on an end side in the longitudinal direction of the
stirring chamber. It is to be noted that the drawing depicted as to
overlap the developing chamber with the stirring chamber shows a
first developing roller 44 and a second developing roller 45.
[0088] Therefore, the powder surface of the developer around the
path 67 of the stirring chamber 64 is lifted up as to reach the
diaphragm 53 as shown with a double-dotted chain line in the
drawing.
[0089] If the agent surface of the developer is lifted up, the
developer may enter into a gap between the first developing roller
and the second developing roller, in substantially the same manner
as in the first embodiment, or namely the SS space 54, so that
consequently, the coating amount of the developer on the second
developing roller is raised, thereby possibly rendering defective
the image density.
[0090] A restricting member 70 is formed to restrict the entry of
the developer by protruding the shape of the diaphragm 53 in
substantially the same manner as in the first embodiment, thereby
preventing the developer from entering into the SS space 54.
[0091] It is to be noted that the restricting member 70 is provided
across substantially the entire region along the longitudinal
direction of the first and second developing rollers because the
entry of the developer into the SS space 54 is done at the entire
region in the longitudinal direction at the developing apparatus
mounted on the developing rotary described above, but in this
embodiment, the restricting member 70 is preferably formed at least
around the path 67 because the developing apparatus is stationally
arranged.
OTHER EMBODIMENTS
[0092] According to the first and second embodiments, exemplified
as the restricting member is the restricting member, unitedly
formed with the container, in which the front end of the diaphragm
formed by protruding the part of the container is widened, but the
member is not limited to this, and can be a separate member. The
shape of the restricting member is not limited to the shape shown
in FIG. 1 and FIG. 2, and other shapes can be possible as far as
the shape restricts the entry of the developer into the SS space as
the above region. It is to be noted that as described in the first
and second embodiments, it is desirable to set the restricting
member as extending along the circumferential surfaces of the first
developing roller and the second developing roller.
[0093] In the above embodiments, exemplified as a developing
apparatus having plural developer carriers is a developing
apparatus having two developer carriers (first developer carrier
and second developer carrier), but the number of the developer
carriers is not limited to this.
[0094] In the above embodiments, exemplified is an image forming
apparatus having the four developing devices, but the used number
is not limited and can be set properly according to the necessity.
Exemplified also is the image forming apparatus capable of forming
color images, but this invention is not limited to this, and this
invention is applicable to a developing apparatus used in an image
forming apparatus capable of forming monochrome images.
[0095] Although in the above embodiments the printer is exemplified
as the image forming apparatus, this invention is not limited to
this, and this invention applicable to image forming apparatuses
such as, e.g., photocopiers, facsimile machines, other image
forming apparatuses such as combined machines combining those
functions, and image forming apparatuses using a transfer carrier
and multiply transferring toners of respective colors to a transfer
material carried on a transfer material carrier in a sequentially
overlapping manner, so that substantially the same advantages can
be obtained in applying this invention to such image forming
apparatuses.
[0096] As described above, according to the above embodiments,
coating of the developer more than the necessary amount on the
developer carrier can be avoided, so that blurs of the developer
and overflows from the developing container can be prevented,
thereby producing developing images with high quality.
* * * * *